U.S. patent application number 14/200264 was filed with the patent office on 2014-09-11 for method and apparatus for protecting a substrate during processing by a particle beam.
The applicant listed for this patent is Carl Zeiss SMS GmbH. Invention is credited to Nicole Auth, Tristan Bret, Michael Budach, Dajana Cujas, Thorsten Hofmann, Petra Spies.
Application Number | 20140255831 14/200264 |
Document ID | / |
Family ID | 51385563 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140255831 |
Kind Code |
A1 |
Hofmann; Thorsten ; et
al. |
September 11, 2014 |
METHOD AND APPARATUS FOR PROTECTING A SUBSTRATE DURING PROCESSING
BY A PARTICLE BEAM
Abstract
The invention refers to a method and apparatus for protecting a
substrate during a processing by at least one particle beam. The
method comprises the following steps: (a) applying a locally
restrict limited protection layer on the substrate; (b) etching the
substrate and/or a layer arranged on the substrate by use of the at
least one particle beam and at least one gas; and/or (c) depositing
material onto the substrate by use of the at least one particle
beam and at least one precursor gas; and (d) removing the locally
limited protection layer from the substrate.
Inventors: |
Hofmann; Thorsten; (Rodgau,
DE) ; Bret; Tristan; (Darmstadt, DE) ; Spies;
Petra; (Mainz, DE) ; Auth; Nicole;
(Gustavsburg, DE) ; Budach; Michael; (Hanau,
DE) ; Cujas; Dajana; (Seeheim-Jugenheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss SMS GmbH |
Jena |
|
DE |
|
|
Family ID: |
51385563 |
Appl. No.: |
14/200264 |
Filed: |
March 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61774799 |
Mar 8, 2013 |
|
|
|
Current U.S.
Class: |
430/5 ; 118/721;
156/345.3 |
Current CPC
Class: |
G03F 1/72 20130101 |
Class at
Publication: |
430/5 ;
156/345.3; 118/721 |
International
Class: |
G03F 1/72 20060101
G03F001/72 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2013 |
DE |
102013203995.6 |
Claims
1. A method for protecting a substrate during a processing by at
least one particle beam, the method comprising the following steps:
a. applying a locally limited protection layer on the substrate; b.
etching the substrate and/or a layer arranged on the substrate by
the at least one particle beam and at least one gas; and/or c.
depositing material onto the substrate by use of the at least one
particle beam and at least one precursor gas; and d. removing the
locally limited protection layer from the substrate.
2. The method according to claim 1, wherein applying the locally
limited protection layer comprises applying the protection layer
adjacent to a portion of the substrate or to the layer to be
processed and/or applying the protection layer in a distance from
the layer within which material is to be deposited onto the
substrate.
3. The method according to claim 1, wherein applying the protection
layer comprises depositing a protection layer which has an etch
selectivity compared to the substrate of larger than 1:1.
4. The method according to claim 1, wherein applying the protection
layer comprises depositing at least one metal containing layer by
use of an electron beam and at least one volatile metal compound on
the substrate.
5. The method according to claim 4, wherein the at least one
volatile metal compound comprises at least one metal carbonyl
precursor gas, and wherein the at least one metal carbonyl
precursor gas comprises at least one of the following compounds:
molybdenum hexacarbonyl (Mo(CO).sub.6), chromium hexacarbonyl
(Cr(CO).sub.6), vanadium hexacarbonyl (V(CO).sub.6), tungsten
hexacarbonyl (W(CO).sub.6), nickel tetracarbonyl (Ni(CO).sub.4),
iron pentacarbonyl (Fe.sub.3(CO).sub.5), ruthenium pentacarbonyl
(Ru(CO).sub.5), or osmium pentacarbonyl (Os(CO).sub.5).
6. The method according to claim 4, wherein the at least one
volatile metal compound comprises a metal fluoride, and wherein the
metal fluoride comprises at least one of the following compounds:
tungsten hexafluoride (WF.sub.6), molybdenum hexafluoride
(MoF.sub.6), vanadium fluoride (VF.sub.2, VF.sub.3, VF.sub.4,
VF.sub.5), and/or chromium fluoride (CrF.sub.2, CrF.sub.3,
CrF.sub.4, CrF.sub.5).
7. The method according to claim 1, wherein the locally limited
protection layer has a thickness of 0.2 nm-1000 nm.
8. The method according to claim 1, wherein depositing material on
the substrate comprises depositing material on the substrate
adjacent to the layer arranged on the substrate.
9. The method according to claim 1, wherein the at least one gas
comprises at least one etching gas.
10. The method according to claim 9, wherein the at least one
etching gas comprises: xenon difluoride (XeF.sub.2), sulfur
hexafluoride (SF.sub.6), sulfur tetrafluoride (SF.sub.4), nitrogen
trifluoride (NF.sub.3), phosphor trifluoride (PF.sub.3), tungsten
hexafluoride (WF.sub.6), molybdenum hexafluoride (MoF.sub.6),
fluorine hydrogen (HF), nitrogen oxygen fluoride (NOF), triphosphor
trinitrogen hexafluoride (P.sub.3N.sub.3F.sub.6) or a combination
of these gases.
11. The method according to claim 1, wherein removing the
protection layer comprises directing the electron beam and at least
one second etching gas onto the protection layer, wherein the at
least one second etching gas comprises an etch selectivity compared
to the substrate of larger than 2:1.
12. The method according to claim 1, wherein removing the
protection layer comprises directing the electron beam and at least
one second etching gas onto the protection layer, wherein the at
least one second etching gas comprises a chlorine containing gas, a
bromine containing gas, an iodine containing gas and/or a gas which
comprises a combination of these halogens.
13. The method according to claim 12, wherein the at least one
second etching gas comprises at least one chlorine containing
gas.
14. The method according to claim 1, wherein removing the
protection layer from the substrate takes place by using a wet
chemical cleaning of the substrate.
15. The method according to claim 1, wherein the substrate
comprises a substrate of a photolithographic mask and/or the layer
arranged on the substrate comprises an absorber layer.
16. The method according to claim 15, wherein the absorber layer
comprises Mo.sub.xSiO.sub.yN.sub.z, wherein 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.2, and 0.ltoreq.z.ltoreq.4/3.
17. A method for removing portions of an absorber layer which is
arranged on portions of a surface of a substrate of a
photolithographic mask, wherein the absorber layer comprises
Mo.sub.xSiO.sub.yN.sub.z, and wherein 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.2, and 0.ltoreq.z.ltoreq.4/3, the method
comprising the step: directing at least one particle beam and at
least one gas on at least one portion of the absorber layer to be
removed, wherein the at least one gas comprises at least one
etching gas and at least one second gas, and wherein the at least
one gas comprises an etching gas and at least one second gas in one
compound.
18. The method according to claim 17, further comprising the step:
changing a ratio of gas flow rates of the at least one etching gas
and the at least one second gas during a time period the at least
one particle beam is directed on the at least one portion of the
absorber layer to be removed.
19. The method according to claim 17, further comprising the step:
changing the composition of the at least one second gas prior to
reaching a layer boundary between the absorber layer and the
substrate.
20. The method according to claim 17, wherein the at least one
second gas comprises an ammonia providing gas.
21. The method according to claim 20, wherein the at least one
ammonia providing gas comprises ammonia (NH.sub.3), ammonium
hydroxide (NH.sub.4OH), ammonium carbonate
(NH.sub.4).sub.2CO.sub.3), diimine (N.sub.2H.sub.2), hydrazine
(N.sub.2H.sub.4), hydrogen nitrate (HNO.sub.3), ammonium
hydrocarbonate (NH.sub.4HCO.sub.3), and/or diammonium carbonate
((NH.sub.3).sub.2CO.sub.3).
22. The method according to claim 20, wherein the at least one
etching gas and the at least one ammonia providing gas are provided
in a compound, and wherein the compound comprises trifluoro
acetamide (CF.sub.2CONH.sub.2), triethylamine trihydrofluoride
((C.sub.2H.sub.5).sub.3N..sub.3HF), ammonium fluoride (NH.sub.4F),
ammonium difluoride (NH.sub.4F.sub.2) and/or tetraammine copper
sulfate (CuSO.sub.4.(NH.sub.3).sub.4).
23. The method according to claim 17, wherein the at least one
second gas comprises at least water vapor.
24. The method according to claim 23, wherein the at least one
second gas comprises at least one ammonia providing gas and water
vapor.
25. The method according to claim 17, wherein the at least one
second gas comprises a metal precursor gas, and wherein the at
least one metal precursor gas comprises at least one of the
following compounds: molybdenum hexacarbonyl (Mo(CO).sub.6),
chromium hexacarbonyl (Cr(CO).sub.6), vanadium hexacarbonyl
(V(CO).sub.6), tungsten hexacarbonyl (W(CO).sub.6), nickel
tetracarbonyl (Ni(CO).sub.4), iron pentacarbonyl
(Fe.sub.3(CO).sub.5), ruthenium pentacarbonyl (Ru(CO).sub.5) and
osmium pentacarbonyl (Os(CO).sub.5).
26. The method according to claim 25, wherein the at least one
second gas comprises a metal carbonyl and water and/or at least one
ammonia providing gas.
27. The method according to claim 17, wherein the at least one
second gas comprises oxygen, nitrogen and/or at least one nitrogen
oxygen compound.
28. The method according to claim 27, wherein the at least one
second gas comprises oxygen, nitrogen and/or at least one nitrogen
oxygen compound, and an ammonia providing gas.
29. The method according to claim 27, wherein the at least one
second gas comprises oxygen, nitrogen and/or at least one nitrogen
oxygen compound, and water vapor.
30. The method according to claim 27, wherein directing the at
least one second gas onto a portion of the absorber layer to be
removed comprises activating the oxygen, the nitrogen and/or the at
least one nitrogen oxygen compound by means of an activation
source.
31. The method according to claim 1, further comprising executing
at least one of the steps of the claim 17.
32. The method according to claim 1, wherein the substrate of the
photolithographic mask comprises a material which is transparent in
the ultraviolet wavelength range, and/or wherein the particle beam
comprises an electron beam.
33. An apparatus for protecting a substrate during a processing by
means of at least one particle beam comprising: a. means for
arranging a locally limited protection layer on the substrate; b.
means for etching the substrate and/or a layer arranged on the
substrate by use of the at least one particle beam and at least one
gas; and/or c. means for depositing material on the substrate by
means of the at least one particle beam and at least one precursor
gas; and d. means for removing the locally limited protection layer
from the substrate.
34. The apparatus according to claim 33, wherein the apparatus is
further configured to execute a method according to claim 1.
35. The method according to claim 33, further comprising means for
generating a second particle beam for activating oxygen, nitrogen
and/or a nitrogen oxygen compound.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional
application 61/774,799, filed on Mar. 8, 2013, and German patent
application 10 2013 203 995.6, filed on Mar. 8, 2013. The contents
of the above-referenced applications are incorporated by reference
in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to a method and apparatus for
protecting a substrate during a processing by a particle beam.
BACKGROUND
[0003] As a result of the constantly increasing integration density
in the semi-conductor industry (Moore's law) photolithographic
masks have to image smaller and smaller structures on wafers. More
and more complex processing procedures are required in order to
generate this small structure dimensions on the wafer. The
processing procedures have in particular to ensure that the
non-processed semiconducting material is not unintentionally
changed and/or modified in an uncontrolled manner by the processing
procedures.
[0004] Photolithographic systems take into account the trend
towards increasing integration density by shifting the exposure
wavelength of lithography apparatus to smaller and smaller
wavelengths. Photolithography systems presently often use an argon
fluoride excimer laser as a light source which emits at a
wavelength of approximately 193 nm.
[0005] At the moment, lithography systems are developed which use
electromagnetic radiation in the extreme ultra violet (EUV)
wavelength range (in the range of 10 nm to 15 nm). These EUV
lithography systems are based on a completely new concept for beam
guiding which exclusively uses reflective optical elements, since
there are presently no materials available which are optically
transparent in the indicated EUV range. The technological
challenges for the development of EUV systems are enormous, and
huge development efforts are necessary in order to bring these
systems to industrial operability.
[0006] It is therefore mandatory to further develop conventional
lithography systems in order to thereby increase the integration
density in the near future.
[0007] Photolithographic masks or exposure masks play a significant
role when imaging smaller and smaller structures in a photoresist
arranged on a wafer. With each further enhancement of the
integration density, it becomes more and more important to improve
the minimum structure size of exposure masks.
[0008] The application of molybdenum doped silicon nitride or
silicon oxynitride layers as absorber material on a substrate of a
photolithographic mask is one possibility to meet these challenges.
Molybdenum doped silicon nitride or molybdenum doped silicon
oxynitride are in the following called MoSi layers.
[0009] The application of a MoSi layer for defining the structure
elements to be imaged into the photoresist allows adjusting that a
certain portion of the electromagnetic radiation incident on the
MoSi layer can penetrate this layer. The molybdenum content
essentially determines the absorption of the MoSi layer. The phase
difference of the radiation penetrating the transparent mask
substrate is adjusted to 180.degree. or .pi. by an etching process
of the mask substrate and/or by a corresponding layer thickness of
the MoSi layer. Thus, a MoSi absorber layer allows imaging
structures with a larger contrast in the photoresist than binary
exposure masks can do. Therefore, smaller and more complex
structures can be represented on a mask substrate compared with
conventional binary absorber layers on the basis of metals. Hence,
a MoSi absorber layer accomplishes a significant contribution to
the improvement of the resolution of an exposure mask.
[0010] The generation of errors cannot be excluded during a mask
fabrication process due to the tiny structure sizes of the absorber
elements and the extreme requirements for exposure masks. The
manufacturing process of photolithographic masks is highly complex
and very time consuming and thus expensive. Therefore, exposure
masks are repaired whenever possible.
[0011] Typically, an ion beam induced (FIB) sputtering or an
electron beam induced etching (EBIE) are used for a local material
removal of excessive material of conventional absorber layers of
exposure masks on the basis of metals, as for example chromium or
titanium. For example, these processes are described in the article
of T. Liang et al: "Progress in extreme ultra violet mask repair
using a focused ion beam", J. Vac. Sci. Technol. B.18 (6), 3216
(2000) and in the patent EP 1 664 924 B1 of the applicant.
[0012] With the progressively decrease of the structure elements of
photolithographic masks further aspects of the absorber structure
elements of photolithographic masks are gaining attention which
have up to now not been important. For example, the durability of
the absorber layer and the durability of the absorber layers in a
chemical cleaning process and/or under radiation with ultraviolet
radiation become more and more important. The molybdenum content of
the MoSi layer has a decisive influence on these properties. It is
a general rule that the lower the molybdenum content is the more
resistive the layers are with respect to their durability regarding
chemical cleaning and UV radiation. Therefore, it is desirable to
also decrease the molybdenum content of MoSi layers when decreasing
the structural elements of the absorber layer.
[0013] On the other hand, the molybdenum content has significant
effects for the repair of mask defects which have been generated
during the manufacturing process. The local removal of excessive
MoSi absorber material by using an electron beam and the presently
usual etching gases becomes more and more difficult with decreasing
molybdenum content of the MoSi layer. In the following, this is
illustrated for an electron beam induced etching process using
xenon difluoride (XeF.sub.2) as an etching gas.
[0014] FIG. 1 shows a segment of a substrate of a mask from which a
rectangular MoSi layer has been etched down to the substrate during
several minutes. The MoSi layer has a molybdenum content in the one
digit percentage range as it is presently usual. The etching
process only causes a moderate surface roughness of the substrate
(dark area) of the photolithographic mask in the area of the
removed MoSi layer. The area of the mask substrate outside of the
etching process does not show a significant modification.
[0015] FIG. 2 shows the segment of the substrate of the mask of
FIG. 1 after etching a MoSi layer having a molybdenum content which
is only half of that of FIG. 1. The etching process for removing
the MoSi layer with the lower molybdenum content needs a multiple
of the time for the MoSi layer of FIG. 1. The etching process which
needs a long time generates an increased roughness of the substrate
around the MoSi layer. This can be recognized from the bright halo
around the ground area of the MoSi layer. Moreover, the etching
process causes significant damages of the mask substrate in the
region of the ground area of the MoSi layer which are recognizable
by the dark spots in this area. The further utilization of the
exposure masks is questionable due to the substrate damages caused
by the etching process.
[0016] Apart from the molybdenum content of the MoSi layer, the
etching behavior significantly depends on the nitrogen content of
the MoSi material system. A larger nitrogen content of the MoSi
layer significantly complicates the removal of excessive MoSi
material.
[0017] The present invention is therefore based on the problem to
indicate methods and an apparatus for protecting a substrate during
processing the substrate and/or a layer arranged on the substrate
by using a particle beam which at least partially avoid the
drawbacks and restrictions mentioned above.
SUMMARY
[0018] According to an aspect of the present invention, in an
embodiment, the method for protecting a substrate during a
processing by at least one particle beam comprises the following
steps: (a) arranging a locally limited protection layer on the
substrate; (b) etching the substrate and/or a layer arranged on the
substrate by using the at least one particle beam and at least one
gas; and/or (c) depositing material onto the substrate by the at
least one particle beam and at least one precursor gas; and (d)
removing the local limited protection layer from the substrate.
[0019] The known problem of riverbedding often occurs in particle
beam induced processing procedures, i.e., material is
unintentionally removed in the area around the etching process or
sputtering process. Apart from the particle beam, the extent of the
occurring riverbedding depends on the gas(es) used in the etching
process.
[0020] Arranging a protection layer around the material to be
removed from the MoSi layer prevents that the etching process can
locally damage the mask substrate independent from its duration and
independent from the used etching gas. Hence, the roughening of the
surface of the substrate illustrated in FIG. 2 can reliably be
avoided. Furthermore, the protection layer also avoids the above
mentioned riverbedding or the local deposition of material on the
substrate during a processing procedure.
[0021] In an aspect, arranging the locally limited protection layer
comprises: arranging the protection layer adjacent to a portion of
the substrate or to the layer which is to be processed and/or
arranging the protection layer in a distance from the layer within
which material is to be deposited onto the substrate.
[0022] According to a further aspect, arranging the protection
layer further comprises: depositing a protection layer which has an
etch selectivity compared to the substrate of larger than 1:1,
preferred larger than 2:1, more preferred larger than 3:1, and most
preferred larger than 5:1.
[0023] In a further aspect, arranging the protection layer further
comprises depositing a layer by use of an electron beam and at
least one volatile metal composition on the substrate.
[0024] Preferably, the volatile metal composition comprises at
least one metal carbonyl precursor gas and the at least one metal
carbonyl precursor gas further comprises at least one of the
following compounds: molybdenum hexacarbonyl (Mo(CO).sub.6),
chromium hexacarbonyl (Cr(CO).sub.6), vanadium hexacarbonyl
(V(CO).sub.6), tungsten hexacarbonyl (W(CO).sub.6), nickel
tetracarbonyl (Ni(CO).sub.4), iron pentacarbonyl
(Fe.sub.3(CO).sub.5), ruthenium pentacarbonyl (Ru(CO).sub.5), and
osmium pentacarbonyl (Os(CO).sub.5).
[0025] Also preferred, the at least one volatile metal composition
comprises a metal fluoride, and the metal fluoride further
comprises at least one of the following compounds: tungsten
hexafluoride (WF.sub.6), molybdenum hexafloride (MoF.sub.6),
vanadium fluoride (VF.sub.2, VF.sub.3, VF.sub.4, VF.sub.5), and/or
chromium fluoride (CrF.sub.2, CrF.sub.3, CrF.sub.4, CrF.sub.5).
[0026] In another aspect, the locally limited protection layer
comprises a thickness of 0.2 nm-1000 nm, preferred 0.5 nm -500 nm,
and most preferred 1 nm-100 nm, and/or has a lateral extension on
the substrate of 0.1 nm-5000 nm, preferred 0.1 nm -2000 nm, and
most preferred 0.1 nm-500 nm.
[0027] In the context of this application a locally limited
protection layer means a protection layer whose lateral extensions
are adapted to the size of a processing location. A processing
location is a defect on the substrate and/or a defect on a layer
arranged on the substrate having excessive or missing material. In
addition to the size of the processing location, the lateral
extensions of a protection layer also depend on the applied
particle beam, its parameters as well as the gas(es) used for the
processing.
[0028] According to a further aspect, depositing material comprises
depositing material on the substrate adjacent to the layer arranged
on the substrate.
[0029] In still a further aspect, the at least one gas comprises at
least one etching gas. Preferably, the at least one etching gas
comprises xenon difluoride (XeF.sub.2), sulfur hexafluoride
(SF.sub.6), sulfur tetrafluoride (SF.sub.4), nitrogen trifluoride
(NF.sub.3), phosphor trifluoride (PF.sub.3), nitrogen oxygen
fluoride (NOF), molybdenum hexafluoride (MoF.sub.6), hydrogen
fluoride (HF), triphosphor trinitrogen hexafluoride
(P.sub.3N.sub.3F.sub.6), or a combination of these gases.
[0030] According to a beneficial aspect, removing the protection
layer comprises directing an electron beam and at least one second
etching gas to the protection layer, wherein the at least second
etching gas has an etch selectivity compared to the substrate of
larger than 1:1, preferred larger than 2:1, more preferred larger
than 3:1, and most preferred larger than 5:1.
[0031] In a further aspect, removing the protection layer comprises
directing the electron beam and at least one second etching gas to
the protection layer, wherein the at least one second etching gas
comprises a chlorine containing gas, a bromine containing gas, an
iodine containing gas and/or a gas which comprises a combination of
these halogens. Preferably, the at least one second etching gas
comprises at least a chlorine containing gas.
[0032] In a further especially preferred aspect, removing the
protection layer of the substrate is effected by means of a wet
chemical cleaning of the substrate.
[0033] According to another aspect, the substrate comprises a
substrate of a photolithographic mask and/or the layer arranged on
the substrate comprises an absorber layer. The absorber layer
preferably comprises Mo.sub.xSiO.sub.yN.sub.z, wherein
0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.2, and
0.ltoreq.z.ltoreq.4/3.
[0034] The material system Mo.sub.xSiO.sub.yN.sub.z comprises four
different compounds as limiting cases:
[0035] (a) molybdenum silicide for y=z=0;
[0036] (b) silicon nitride or silicon nitrogen layer systems for
x=y=0;
[0037] (c) molybdenum-doped silicon oxide for z=0; and
[0038] (d) molybdenum-doped silicon nitride for y=0.
[0039] According to a further embodiment of the present invention,
the method for removing portions of an absorber layer, which are
arranged on portions of a surface of a substrate of a
photolithographic mask, wherein the absorber layer comprises
Mo.sub.xSiO.sub.yN.sub.z and wherein 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.2 and 0.ltoreq.z.ltoreq.4/3, comprises the step:
directing at least one particle beam and at least one gas on the at
least one portion of the absorber layer to be removed, wherein the
at least one gas comprises at least one etching gas and at least
one second gas, or wherein the at least one gas comprises the at
least one etching gas and at least one second gas in one
compound.
[0040] In the above described alternative of a removal process of
excessive MoSi absorber material, the occurrence of damages of the
mask substrate is prevented in that the etching process is
accelerated by the addition of a second gas, or the etching process
on the substrate material is slowed down. Alternatively, both
etching rates can be slowed down, wherein, however, the etching
rate on the substrate is significantly stronger slowed down than
the etching rate of the MoSi material, so that in total the effect
of the secondary particles on the substrate is limited. The second
gas or its composition can be adjusted to the material composition
of the respective MoSi layer.
[0041] A further beneficial aspect comprises changing a ratio of
gas flow rates of the at least one etching gas and the at least one
second gas during a time period when the at least one particle beam
and the at least one gas are directed on the at least one portion
of the absorber layer to be removed. Preferably, the composition of
the at least one second gas is changed prior to reaching a layer
boundary between the absorber layer and the substrate.
[0042] In another aspect, the at least one second gas comprises a
gas which provides ammonia. Preferably, the at least one ammonia
providing gas comprises ammonia (NH.sub.3), ammonium hydroxide
(NH.sub.4OH), ammonium carbonate ((NH.sub.4).sub.2CO.sub.3),
diimine (N.sub.2H.sub.2), hydrazine (N.sub.2H.sub.4), hydrogen
nitride (HNO.sub.3), ammonium hydrogen carbonate
(NH.sub.4HCO.sub.3) and/or diammonia carbonate
((NH.sub.3).sub.2CO.sub.3).
[0043] According to a further aspect, the at least one etching gas
and the at least one ammonia providing gas is provided in one
compound and the compound comprises trifluoro acetamide
(CF.sub.2CONH.sub.2), triethylamine trihydro fluoride
((C.sub.2H.sub.5).sub.3N..sub.3HF), ammonium fluoro ride
(NH.sub.4F), ammonium difluoride (NH.sub.4F.sub.2) and/or
tetrammine copper sulfate (CuSO.sub.4.(NH.sub.3).sub.4).
[0044] According to another aspect, the at least one second gas
comprises at least water vapor.
[0045] In a beneficial aspect, the at least one second gas
comprises an ammonia providing gas and water vapor.
[0046] According to a beneficial aspect, the at least one second
gas comprises at least one metal precursor gas, and the at least
one metal precursor gas comprises one of the following compounds:
molybdenum hexacarbonyl (Mo(CO).sub.6), chromium hexacarbonyl
(Cr(CO).sub.6), vanadium hexacarbonyl (V(CO).sub.6), tungsten
hexacarbonyl (W(CO).sub.6), nickel tetracarbonyl (Ni(CO).sub.4),
iron pentacarbonyl (Fe.sub.3(CO).sub.5), ruthenium pentacarbonyl
(Ru(CO).sub.5) and/or osmium pentacarbonyl (Os(CO).sub.5).
[0047] In a beneficial aspect, the at least one second gas
comprises at least one metal carbonyl and water vapor, and/or at
least an ammonia providing gas.
[0048] According to a preferred aspect, the at least one second gas
comprises oxygen, nitrogen and/or at least one nitrogen oxygen
compound. According to a further aspect, the at least one second
gas comprises oxygen, nitrogen and/or at least one nitrogen oxygen
compound and an ammonia providing gas. According to a further
aspect, the at least one second gas comprises oxygen, nitrogen,
and/or at least one nitrogen oxygen compound and water vapor.
[0049] In still another aspect, directing the at least one second
gas onto the portion of the absorber layer to be removed comprises
activating the oxygen, the nitrogen and/or the at least one
nitrogen oxygen compound with an activating source.
[0050] Nitrogen oxide (NO) radicals can lead to an amplification of
the oxidation of silicon nitride at the surface. Thereby, the
etching rate of fluorine-based reagents can significantly be
accelerated (cf. Kastenmeier et. al.: "Chemical dry etching of
silicon nitride and silicon dioxide using CF.sub.4/O.sub.2/N.sub.2
gas mixtures", J. Vac. Sci. Technol. A (14(5), p. 2802-2813,
September/August 1996).
[0051] According to a beneficial aspect, a method for protecting a
substrate during a processing by use of at least one particle beam
comprises the following steps: (a) arranging a locally limited
protection layer on the substrate; (b) etching the substrate and/or
a layer arranged on the substrate by use of the at least one
particle beam and at least one gas; and/or (c) depositing material
onto the substrate by use of the at least one particle beam and at
least one precursor gas; and (d) removing the locally limited
protection layer from the substrate. Further, the method comprises
performing at least one step according to one of the above
indicated aspects.
[0052] The combination of arranging a locally limited protection
layer and the application of a gas which comprises an etching gas
and a second gas, on the one hand, enables by the adjustment of two
independent parameters to protect the mask substrate surrounding a
defect, and, on the other hand, enables to protect the area of the
substrate below the defect from damages by the processing procedure
of the absorber layer. The second gas allows thereby the
optimization of the etching process without having to fear damages
of the substrate. Thus, the second gas can exclusively be selected
for optimizing the etching process, and for avoiding substrate
damages below the defect without any tradeoff.
[0053] In a further aspect, the substrate of the photolithographic
mask comprises a material which is transparent in the ultraviolet
wavelength range and/or the particle beam comprises an electron
beam. In addition to an electron beam, an ion beam is also
beneficial. In this process, ions beams are preferred which are
generated by means of a gas field ion source (GFIS), and a noble
gas, such as helium (He), neon (Ne), argon (Ar), krypton (Kr)
and/or xenon (Xe).
[0054] The application of the above defined method is not
restricted to a substrate of a photolithographic mask. Rather, the
method allows reliably protecting all semiconductor materials
during a processing step and/or during a correction of local
defects. Moreover, a locally limited protection layer can generally
be used for protecting any materials, such as an isolator, a
semiconductor, a metal, or a metal compound during a particle beam
induced local processing procedure of the material. Finally, the
above discussed method can also be used for removing defects of
reflective masks for the extreme ultraviolet (EUV) wavelength
range.
[0055] A further aspect of the present invention refers to an
apparatus for protecting a substrate during a processing by means
of at least one particle beam, wherein the apparatus comprises: (a)
means for arranging a locally limited protection layer on the
substrate; (b) means for etching the substrate and/or a layer
arranged on the substrate by means of the at least one particle
beam and at least one gas; and/or (c) means for depositing material
on the substrate by means of the at least one particle beam and at
least one precursor gas; and (d) means for removing the locally
limited protection layer from the substrate.
[0056] According to another aspect, the apparatus is configured to
execute a method according to any one of the above indicated
aspects.
[0057] According to a further aspect, the apparatus comprises
further means for generating a second particle beam for activating
oxygen, nitrogen and/or a nitrogen oxygen compound.
DESCRIPTION OF THE DRAWINGS
[0058] In the following detailed description presently preferred
application examples of the invention are described with respect to
the drawings, wherein
[0059] FIG. 1 shows a segment of a top view of a substrate of a
mask from which a MoSi layer has been removed, wherein the
molybdenum content of the MoSi layer was in a one digit percent
range;
[0060] FIG. 2 represents a segment of a top view of a substrate of
an exposure mask from which the MoSi layer has been etched off,
wherein the molybdenum content of the MoSi was approximately half
of that of FIG. 1;
[0061] FIG. 3 depicts a cross section through schematic
representation of an apparatus for correcting absorber defects of
photolithographic masks;
[0062] FIG. 4 shows a schematic top view of a segment of a
line-space structure made from absorber material in which one line
or stripe has a defect at which excessive absorber material has
been deposited;
[0063] FIG. 5 schematically represents the arrangement of a local
limy ited protection layer for the defect of FIG. 4;
[0064] FIG. 6 schematically represents the etching of the defect of
FIG. 5 by use of an electron beam and an etching gas;
[0065] FIG. 7 schematically illustrates etching of the defect of
FIG. 5 by use of an electron beam, an etching gas and an ammonia
providing gas;
[0066] FIG. 8 represents a segment of a mask from which a
rectangular MoSi layer having a low molybdenum content has been
removed by use of an electron beam, XeF.sub.2 as an etching gas,
and ammonium hydroxide (NH.sub.4OH);
[0067] FIG. 9 schematically illustrates etching the defect of FIG.
5 by use of an electron beam, an etching gas, an ammonia providing
gas, and water vapor;
[0068] FIG. 10 schematically represents etching the defect of FIG.
5 by use of an electron beam, an etching gas, an ammonia providing
gas and nitrogen monoxide radicals;
[0069] FIG. 11 schematically reproduces etching the defect of FIG.
5 by the use of an electron beam, an etching gas, a metal carbonyl,
an ammonia providing gas, and/or water;
[0070] FIG. 12 shows FIGS. 7 and 9-11 after finalization of the
removal of the defect of FIG. 5;
[0071] FIG. 13 schematically represents an etching process for
removing the locally limited protection layer of FIG. 12;
[0072] FIG. 14 schematically depicts the section of the mask of
FIG. 13 after removing the protection layer;
[0073] FIG. 15 shows a schematic top view of a segment of a
line-space structure made from absorbing material, at which a line
or stripe has a defect of missing absorber material;
[0074] FIG. 16 represents a cross section through a schematic
representation of a photolithographic mask during the process of
arranging a locally limited protection layer;
[0075] FIG. 17 shows a cross section through the mask of FIG. 16
during a deposition process of missing absorber material;
[0076] FIG. 18 represents the cross section through the mask of
FIG. 17 during removing the locally limited protection layer;
and
[0077] FIG. 19 indicates a cross section through the mask of FIG.
18 after the removal of the locally limited protection layer.
DETAILED DESCRIPTION
[0078] In the following preferred embodiments of the inventive
method and the inventive apparatus are described in more detail.
These are explained using the example of processing defects of
photolithographic masks. However, the inventive method and the
inventive apparatus are not limited to the application of
photolithographic masks. Rather, they can be utilized for
processing semiconductor materials during the manufacturing process
and/or during a repair process. It is also possible to use a
locally limited protection layer for protecting arbitrary materials
during a local processing by the use of a particle beam.
[0079] FIG. 3 shows a cross section of a schematic representation
of preferred components of an apparatus 1000 which can be used for
repairing local defects of an absorber structure of a mask, and
which can at the same time prevent a substrate of the mask from
damages during a repairing process. The exemplary apparatus woo of
FIG. 3 is a modified scanning electron microscope (SEM). An
electron gun 1018 generates an electron beam 1027 and the beam
forming and beam imaging elements 1020 and 1025 direct the focused
electron beam 1027 either on the substrate 1010 of an exposure mask
1002, or to an element of the absorber structure arranged on the
surface 1015 (not shown in FIG. 3).
[0080] The substrate 1010 of the mask 1002 is arranged on the
sample stage 1005. The sample stage 1005 comprises an offset
slide--which is not represented in FIG. 3--which allows that the
mask 1002 can be shifted in a plane perpendicular to the electron
beam 1027 so that the defect of the absorber structure of the mask
1002 is below the electron beam 1027. The sample stage 1005 can
further include one or several elements by the use of which the
temperature of the substrate 1010 of the mask 1002 can be set to a
predetermined temperature and can be controlled at a predetermined
temperature (not indicated in FIG. 3).
[0081] The exemplary apparatus 1000 of FIG. 3 uses an electron beam
1027 as a particle beam. The electron beam 1027 can be focused on a
small spot with a diameter of less than 10 nanometers on the
surface 1015 of the mask 1002. The energy of the electrons
impinging on the surface 1015 of the substrate 1010 or onto an
element of the absorber structure can be varied across a large
energy range (from a few eV up to 50 keV). When impinging on the
surface 1015 of the substrate 1010, the electrons do not cause
significant damages of the substrate surface 1015 due to their
small mass.
[0082] The usage of the method defined in this application is not
limited to the usage of an electron beam 1027. Rather, any particle
beam can be used which is capable to induce a local chemical
reaction of a precursor gas at the position at which the particle
beam hits the mask 1002 and where a corresponding gas is provided.
Examples of alternative particle beams are ion beams, metal beams,
molecular beams and/or photon beams.
[0083] It is also possible to use two or more particle beams in
parallel. A laser system 1080 is incorporated in the apparatus 1000
exemplarily represented in FIG. 3 which generates a laser beam
1082. Thus, the apparatus 1000 allows simultaneously applying an
electron beam 1027 in combination with a photon beam 1082 to the
mask 1002. Both beams 1027 and 1082 can continuously be provided or
in the form of pulses. Moreover, the pulses of the two beams 1027
and 1082 can simultaneously partially overlap or can intermediary
react on the reaction site. The reaction site is the position at
which an electron beam 1027 induces alone or in combination with
the laser beam 1082 a local chemical reaction of a precursor
gas.
[0084] Additionally, the electron beam 1027 can be used for
scanning across the surface 1015 for recording an image of the
surface 1015 of the substrate 1010 of the mask 1002. A detector
1030 for backscattered and/or secondary electrons which are
generated by the electrons of the incident electron beam 1027
and/or by the laser beam 1082 provides a signal which is
proportional to the composition of the substrate material 1110, or
to the composition of the material of the elements of the absorber
structure. Defects of the absorber structure elements of the mask
1002 can be determined from the image of the surface 1015 of the
substrate 1010. Alternatively, defects of the absorber structure of
a mask 1002 can be determined by exposing a wafer and/or by the use
of the recording of one or several air images for example
determined by means of an AIMS.TM..
[0085] A computer system 1040 can determine an image of the surface
1015 of the substrate 1010 of the mask 1002 on the basis of a
signal of the detector 1030 obtained from a scan of the electron
beam 1027 and/or the laser beam 1082. The computer system 1040 can
include algorithms realized in hardware and/or software which allow
determining an image of the surface 1015 of the substrate 1010 of
the mask 1002 from the data signal of the detector 1030. A monitor
connected with the computer system 1040 can represent the
calculated image (not shown in FIG. 3). The computer system 1040
can also indicate the signal data of the detector 1030 and/or can
store the calculated image (also not indicated in FIG. 3). The
computer system 1040 can also control and regulate the electron gun
1018 and the beam forming and beam imaging elements 1020 and 1025
as well as the laser system 1080. Moreover, the computer system
1040 can also control the movement of the sample stage 1005 (not
illustrated in FIG. 3).
[0086] The electron beam 1027 incident on the surface 1015 of the
substrate 1010 of the mask 1002 can charge the substrate surface
1015. In order to reduce the effect of the charge accumulation by
the electron beam 1027, an ion gun 1030 can be used for irradiating
the substrate surface 1015 with ions having low energy. For
example, an argon ion beam having kinetic energy of some hundreds
of volts can be used for neutralizing the substrate surface 1015.
The computer system 1040 can also control the ion beam source
1035.
[0087] A positive charge distribution can accumulate on the
isolating surface 1015 of the substrate 1010 if a focused ion beam
is used instead of an electron beam 1027. In this case, an electron
beam can be used for irradiating the substrate surface 1015 in
order to reduce the positive charge distribution on the substrate
surface 1015.
[0088] The exemplary apparatus 1000 of FIG. 3 preferably comprises
six different storage containers for different gases or precursor
gases for processing one or several defects of the absorber
structure arranged on the surface 1015 of the substrate 1010. The
first storage container 1050 stores a first precursor gas or a
deposition gas which is used in combination with the electron beam
1027 for generating a protection layer around the defect of an
absorber element. The second storage container 1055 includes a
chlorine containing etching gas by the use of which the protection
layer is removed from the surface 1015 of the substrate 1010 of the
mask 1002 after the finalization of the repairing processes for the
absorber defect.
[0089] The third storage container 1060 stores an etching gas, for
example xenon difluoride (XeF.sub.2) which is used for locally
removing excessive absorber material. The fourth storage container
1065 stockpiles a precursor gas for locally depositing missing
absorber material on the surface 1015 of the substrate 1010 of the
exposure mask 1002. The fifth 1070 and the sixth storage container
1075 contain two further different gases which can be mixed to the
etching gas stored in the third storage container 1060 as needed.
Moreover, the apparatus 1000 allows installing further storage
containers and gas supplies as needed.
[0090] Each storage container has its own valve 1051, 1056, 1061,
1066, 1071, 1076 in order to control the amount of gas particles
provided per time unit or the gas flow rate at the place where the
electron beam 1027 impinges onto the substrate 1010 of the mask
1002. Additionally, each storage container 1050, 1055, 1060, 1065,
1070, 1075 has its own gas supply 1052, 1057, 1062, 1067, 1072,
1077, which ends with a nozzle close to the point of impact of the
electron beam 1027 on the substrate 1010. The distance between the
point of impact of the electron beam 1027 on the substrate 1010 of
the mask 1002 and the nozzles of the gas supplies 1052, 1057, 1062,
1067, 1072, 1077 is in the range of some millimeters. However, the
apparatus 1000 of FIG. 3 also allows the arrangement of gas
supplies whose distances to the point of impact of the electron
beam 1027 is smaller than one millimeter.
[0091] In the example presented in FIG. 3 the valves 1051, 1056,
1061, 1066, 1071, 1076 are implemented close to the storage
container. In an alternative embodiment all or some of the valves
1051, 1056, 1061, 1066, 1071, 1076 can be arranged close to the
respective nozzle (not shown in FIG. 3). Moreover, the gases of two
or more storage containers can be provided by means of a common gas
supply; this is also not illustrated in FIG. 3.
[0092] Each of the storage containers can have its own element for
an individual temperature setup and control. The temperature
setting allows both a cooling and a heating of each gas.
Additionally, each of the gas supplies 1052, 1057, 1062, 1067,
1072, 1077 can also have an individual element for setting and
controlling the supply temperature of each gas at the reaction site
(also not indicated in FIG. 3).
[0093] The apparatus 1000 of FIG. 3 has a pumping system in order
to generate and to maintain the required vacuum. Prior to starting
a processing procedure, the pressure in the vacuum chamber 1007 is
typically in the range of 10.sup.-5 Pa to 210.sup.-4 Pa. At the
reaction site, the local pressure can typically increase up to a
range of approximately 10 Pa.
[0094] The suction device 1085, schematically represented in FIG.
3, is an important part of the gas supply system. The suction
device 1085 in combination with the pump 1087 enables that the
fragments, which are generated by the decomposition of a precursor
gas or parts of the precursor gas which are not needed for the
local chemical reaction--as for example carbon monoxide, which
originates from the electron beam induced decomposition of metal
carbonyls--are essentially extracted at the place of the generation
from the vacuum chamber 1007 of the apparatus 1000. A contamination
of the vacuum chamber 1007 is avoided since gas components which
are not needed are locally extracted from the vacuum chamber 1007
at the position of the incidence of the electron beam 1027 and/or
the laser beam 1082 on the substrate 1010 before they are
distributed and before they are deposited.
[0095] Preferably, an electron beam 1027 is exclusively used for
initializing the etching reaction in the exemplary apparatus 1000
of FIG. 3. The accelerating voltage of the electrons is in a range
of 0.01 keV to 50 keV. The current of the applied electron beam
varies in an interval between 1 pA and 1 nA. The laser system 1080
provides an additional and/or alternative energy transfer mechanism
by the use of the laser beam 1082. The energy transfer mechanism
can for example selectively activate the precursor gas or can
selectively activate components or fragments generated by the
decomposition of the precursor gas in order to efficiently support
local repairing processes of the absorber structure elements.
[0096] FIG. 4 schematically shows a segment of a substrate 1110 of
an exposure mask 1100. A line-space structure of absorber material
1120, 1125 is arranged on a surface 1115 of the substrate 1110. The
right line or stripe 1125 comprises an extension defect 1130 having
excessive absorber material. The dotted line 1135 shows the cutting
line of the cut or the cross-section through the segment of the
exposure mask 1100 of FIG. 4, wherein the cross section is
represented in FIG. 5.
[0097] The defect 1130 represented in the example of FIG. 5 has
accidentally the same height as the absorber element 1125. However,
this is no requirement for repairing extension defects of the
absorber structure 1120, 1125 of the mask 1100. Rather, the
repairing process described in the following can correct defects
which are lower or higher than the absorber structure elements
1120, 1125.
[0098] In a first step, a protection layer 1150 is deposited on the
surface 1115 of the substrate 1100 around the defect 1130. For this
purpose, an electron beam 1140 is focused on the surface 1115 of
the substrate 1110 of the mask 1100. The electron beam 1140 is
scanned across the portion of the surface 1150 onto which the
locally limited protection layer 1150 is to be deposited. A
precursor gas is locally provided in parallel with the electron
beam 1140. In principle, any deposition precursor gas can be used.
Volatile metal compounds are preferred since thereby locally
limited protection layers 1150 can be deposited which can easily
and residue-free be removed from the substrate after the processing
procedure. Metal carbonyls are beneficial from the multitude of
volatile metal compounds.
[0099] A protection layer 1150 should simultaneously fulfill three
essential requirements: it should be possible to apply the
protection layer 1150 in a defined form on the mask substrate 1110
without significant complexity of the instruments. The protection
layer 115o has to essentially resist the processing procedure of
the MoSi absorber layer. Finally, it should be possible to again
essentially residue-free remove the protection layer 1150 from the
substrate 1110 of an exposure mask 1100. The expression essentially
means here as well as on other passages of the description a change
of the mask which does not compromise the functionality of the
mask.
[0100] As it is already indicated above, metal carbonyls 1145 are
especially well suited for depositing a protection layer 1150. Best
results could up to now be reached with the metal carbonyl
precursor gas molybdenum hexacarbonyl (Mo(CO).sub.6). Other metal
carbonyls have also successfully been used, as for example chromium
hexacarbonyl (Cr(CO).sub.6).
[0101] The energy-transferring action of the electron beam 1140
splits the carbon monoxide (CO) ligands from the central metal atom
at the position of the chemical reaction, i.e., at the position at
which the electron beam 1140 impinges on the surface of the
substrate. The suction device 1085 removes a portion of the CO
molecules from the reaction site. The metal atom of a precursor gas
molecule deposits a deposit at the reaction site on the surface
1115 of the substrate 1110 of the mask 1100, as the case may be
with one or more CO molecules, and thus forms the protection layer
1150.
[0102] The parameters of the electron beam 1140 during the
deposition process depend from the used precursor gas. For example,
for the precursor gas molybdenum hexacarbonyl (Mo(CO).sub.6) good
results are obtained by using electrons having a kinetic energy in
the range of 0.2 keV to 5.0 keV and having a beam current between
0.5 pA and 100 pA. There are no specific requirements to the focus
of the electron beam for depositing the protection layer.
[0103] Molybdenum hexacarbonyl is conveyed to the reaction site
through the gas supply 1052 with a gas flow rate of 0.01 sccm to 5
sccm (standard cubic centimeter per minute) which is adjusted and
controlled by the valve 1058. Alternatively, the amount of gas
provided at the reaction site can be controlled and regulated by
the temperature of Mo(CO).sub.6 or more generally of metal
carbonyls, and thus can be controlled or regulated by the
pressure.
[0104] In addition to the material used for the protection layer
1150 the thickness of the protection layer 1150 to be deposited
also depends from the subsequent processing procedure against which
the protection layer 1150 has to protect the surface 1115 of the
substrate 1110. The protection layer 1150, for example a
Mo(CO).sub.6 layer, should have a thickness between 1 nm and 5 nm
in order to provide protection against a processing of the defect
1130 by means of an electron beam in a subsequent removing or
etching process.
[0105] The requirements to the protection layer are lower when
depositing absorber material. In this case, it is sufficient that
the deposited protection layer is free from pinholes so that a
layer thickness of approx. 1 nm is sufficient.
[0106] The size and the form of the protection layer 1150 can be
derived from the process conditions of the subsequent processing
procedure. The protection layer 1150 can be produced by scanning
the electron beam 1140 across the determined surface 1115 of the
substrate 1110 when the metal carbonyl precursor gas 1145 is
simultaneously provided.
[0107] The protection layer 1150 can comprise two or several
layers. The lowest layer which is in contact with the surface 1115
of the substrate 1110 can provide a defined adhesion to the
substrate 1110.
[0108] The second or the further higher layers of the locally
limited protection layer 1150 can provide a defined resistance
against to the subsequent adjacent processing procedure.
Alternatively, the composition of the protection layer 1150 can be
changed across its thickness or depth. For this purpose, in
addition to the metal carbonyl precursor gas from the storage
container, a second precursor gas can locally be supplied at the
reaction site, for example by the sixth storage container 1175.
[0109] FIG. 6 illustrates an exemplary removal process 1200 of
excessive materials of the defect 1130 by means of an electron beam
1240 and an etching gas 1245. In the example of FIG. 6, the
elements of the absorber structure 1120, 1125 as well as the defect
1130 consist of Mo.sub.xSiO.sub.yN.sub.z, with:
0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.2.0,
0.ltoreq.z.ltoreq.4/3; this material system is in the following
abbreviated with MoSi. The application of an electron beam 1240 is
beneficial in that one particle beam can be used for forming the
protection layer 1150 and for removing excessive MoSi material.
[0110] For example, xenon difluoride (XeF.sub.2) can be used as an
etching gas 1245. Further examples of possible etching gases are
sulfur hexafluoride (SF.sub.6), sulfur tetrafluoride (SF.sub.4),
nitrogen trifluoride (NF.sub.3), phosphor trifluoride (PF.sub.3),
tungsten hexafluoride (WF.sub.6), hydrogen fluoride (HF), nitrogen
oxygen fluoride (NOF), triphosphor trinitrogen hexafluoride
(P.sub.3N.sub.3F.sub.6), or a combination of these etching gases.
It is also possible to extend the etching chemicals to other
halogens, as for example chlorine (Cl.sub.2), bromine (Br.sub.2),
iodine (I.sub.2) or their compounds, as for example iodine chlorine
(ICI) or chlorine hydrogen (HCl).
[0111] An electron beam induced etching process is difficult for
MoSi layers having a low molybdenum content. A very low etching
rate is achieved with the above indicated etching gases 1245 and an
electron beam 1240 if the MoSi material additionally has a high
content of nitrogen. The secondary electrons 1260 act on the
protection layer 1150 during a long time period, and can thus
damage the protection layer 1150.
[0112] Etch selectivity is an important parameter characterizing an
etching process. The etch selectivity is defined by the ratio of
the etching rate of a first material, in general the material to be
etched, to the etching rate of a second material, usually the
material which is not to be etched. The larger this ratio is the
more selective the etching process is, and the simpler it is to
reproducibly achieve the required etching results. Applied to the
etching process of FIG. 6 this means that an etch selectivity would
be high if the etching process would etch the material of the MoSi
layer 1130 with a much higher etching rate than the substrate 1110
of the mask 1100.
[0113] The combination of electron beam 1250 and etching gas 1245
would then remove the defect 1130 with a large rate, and the
process would considerably be slowed down when reaching the layer
boundary to the surface 1115 of the substrate 1110, or ideally the
process would come to a standstill.
[0114] In the example of FIG. 6, the etch selectivity is in the
range 1:7. This means that the electron beam 1240 and the etching
gas 1245 etch the substrate 1110 of the mask 1100 much faster than
the MoSi material of the defect 1130. At least two consequences
arise from this result. Without the protection layer 1150 already
the contribution of the forward scattered electrons 1260 would lead
to a damage of the substrate 1110 of the mask 1100 which is in the
same order of magnitude as the thickness of the absorber layer to
be removed. The protection layer 1150 efficiently prevents this
etching process.
[0115] The etching gases, which are presently used as a standard
for removing MoSi material, create a kind of crater landscape on
the etched surface of the defect in the course of a time consuming
etching process. This is indicated in FIG. 6 by the numeral 1242.
When reaching the layer boundary between the defect 1130 and the
underlying substrate either a portion of the defect 1130 is not
removed, if the etching process is stopped as soon as the deepest
crater of the defect has reached the substrate surface 1115, or the
etching process forms an amplified crater landscape in the mask
substrate 1150, if the etching process is only ended after the
complete removal of the defect 1130.
[0116] FIG. 2 shows the result of the etching process of FIG. 6 for
a rectangular MoSi layer having low molybdenum content. The etching
process 1200 of FIG. 6 has transformed the roughness 1242 of the
defect 1130 into the mask substrate 1110 below the MoSi layer.
[0117] By the addition of ammonia providing gases when etching MoSi
layers, the crater landscape or the roughness 1242 can
significantly be reduced. FIG. 7 illustrates this fact. An ammonia
providing gas or a combination of different ammonia providing gases
can for example be provided by the fifth or sixth storage container
1070 and/or 1075 by means of the gas supplies 1072, 1077 at the
reaction site, and can be controlled by means of their valves 1071
and/or 1076.
[0118] In addition to ammonia (NH.sub.3), ammonium hydroxide
(NH.sub.4OH) and/or aromatic salt ((NH.sub.4).sub.2CO.sub.3) can
also be used as ammonia providing gases as well as similar
substances, as for example ammonium carbonate
((NH.sub.3).sub.2CO.sub.3), ammonium hydrogen carbonate
(NH.sub.4HCO.sub.3), diimine (N.sub.2H.sub.2), hydrazine
(N.sub.2H.sub.4), hydrogen carbonate (HNO.sub.3). On the one hand,
these gases slightly accelerate etching of MoSi material of the
defect 1130 and, on the other hand, slow down the etching process
of the substrate 1110 of the mask 1100. The slow-down is
approximately a factor of 2 and the acceleration reaches
approximately 40% for typical process parameters of the etching
process depicted in FIG. 7. Thus, the etch selectivity in total
improves from approximately 1:7 in the etching process 1200 of FIG.
6 to now 1:2.5. However, thereby the etch selectivity is still in
the inverse regime. This means, the electron beam 1440 and the
combination of the precursor gases 1445 still etch the substrate
1110 faster than the MoSi material of the defect 1130.
[0119] Due to the smooth etching behavior of the defect 1130, which
is depicted in FIG. 7, a combination of the gases 1445 comprising
an etching gas 1245 (XeF.sub.2 in the example of FIG. 6) and at
least one ammonia providing gas in combination with the detection
of back scattered and/or secondary electrons as discussed in the
context of FIG. 3 lead to the removal of the exemplary defect 1130
within a predetermined specification.
[0120] The ratio of the gas flow rates of the etching gas 1245 and
the ammonia providing gas can be varied during the etching process
1400. A composition of the MoSi material which changes along the
depth of the defect 1130 can thus be taken into account. On the
other hand, the etching rate of the defect 1130 and the roughness
of the substrate surface 1150 can thus be optimized in the region
of the defect 1130 to be removed.
[0121] FIG. 8 shows the effect of the addition of an ammonia
providing gas for the removal of a MoSi layer having low molybdenum
content. In the etching process, whose result is represented in
FIG. 8, ammonium hydroxide (NH.sub.4OH) has been admixed to the
etching gas XeF.sub.2. The energy of the electron beam 1440 was in
a range between 0.1 keV and 5.0 keV in the exemplary correction
process of FIG. 8. The gas flow rates of XeF.sub.2 and NH.sub.4OH
have been in the range of 0.05 sccm up to 1 sccm and from 0.01 sccm
to 1 sccm, respectively.
[0122] In a modified process control, the gases 1445, i.e., the
etching gas 1245 and the ammonia providing gas are provided in one
chemical compound, i.e., within one gas molecule at the reaction
site. For this purpose, for example the compounds trifluorine
acetamide (CF.sub.2CONH.sub.2), triethylamine trihydrofluoride
((C.sub.2H.sub.5).sub.3N..sub.3HF), ammonium fluoride (NH.sub.4F),
ammonium difluoride (NH.sub.4F.sub.2) and/or tetrammine copper
sulfate (CuSO.sub.4.(NH.sub.3).sub.4) can be used. The storage is
facilitated by the application of a precursor gas which
simultaneously provides an etching gas and an ammonia providing
gas. Moreover, the gas supply and control is also facilitated,
since only one single gas is needed instead of a mixture of several
gases.
[0123] The etch selectivity can be increased in the etching process
1400 depicted in FIG. 7 if water or water vapor is additionally
supplied to the reaction site in addition to the etching gas 1245
and an ammonia providing gas. FIG. 9 illustrates the etching
process 1600 which is achieved in this way. On the one hand, the
addition of water to the mixture of gases 1645 leads to a sharper
edge of the MoSi absorber element 1125 along the defect 1130 to be
removed. On the other hand, water vapor significantly improves the
etch selectivity from approximately 1:2.5 (the etching process 1300
of FIG. 7) to about 1.7:i. Hence, the etching process, represented
in FIG. 9, leaves the inverse regime. The increase of the etch
selectivity is achieved by means of a slow-down of the etching
rate. The etching rate of the MoSi layer of defect 1130 reduces by
approximately a to factor of two, whereas the etching rate of the
mask substrate 1155 is slowed down by approximately an order of
magnitude with respect to the etching process 1400 of FIG. 7.
[0124] Thus, the etching process 1600 of FIG. 9, whose second gas
1645 comprises a combination of three substances (etching gas 1245,
an ammonia providing gas and water), at least in principle can do
without the protection layer 1150. However, it is beneficial not to
go without the protection layer 1150 in the etching process 1600 of
FIG. 9 due to the distinct affinity of ammonia supported processes
to riverbedding, in particular if the MoSi material of the defect
1130 has a low molybdenum concentration and/or has a high fraction
of nitrogen.
[0125] In a further variation of the etching process of FIG. 7,
nitrogen monoxide (NO) is admixed to the etching gas 1245 instead
of water. The etching process 1700 represented in FIG. 11 uses as a
second gas 1745 a mixture of the components: etching gas 1245 and
NO. The NO radicals are activated at the reaction site by the use
of the electron beam 1740 and/or by means of the laser beam
1082.
[0126] As already explained in the third part of the description,
NO radicals significantly increase the etching rate of silicon
nitride without attacking the silicon oxygen connections of the
quartz substrate 1110 of the mask 1100. Thus, the selectivity of
the etching process 1700 of FIG. 10 is again increased compared
with the etching process 1600 of FIG. 9. As a consequence, the
etching process 1700 of FIG. 11 does in principle not need the
protection layer 1150.
[0127] In a modified etching process, an ammonia providing gas is
additionally added to the mixture of gases 1745 in addition to the
etching gas 1245 and nitrogen monoxide. The NO radicals can again
be activated as described in the previous section. Details of the
composition of the MoSi material to be removed determine whether
the modified etching process can be performed without the
protection layer 1150.
[0128] In a further modified processing procedure of the etching
process 1700 of FIG. 10, nitrogen (N.sub.2) and oxygen (O.sub.2)
are provided at the reaction site instead of nitrogen monoxide.
Nitrogen and oxygen are again activated at the reaction site by
means of the electron beam 1740 and/or by the use of the laser beam
1082 of the laser system 1080 so that nitrogen and oxygen
preferably react to NO. The further sequence of the etching process
then takes place as described in the previous section.
[0129] As it has already been explained in the context of FIG. 2,
the etching rate of a MoSi layer decreases with a decreasing
fraction of molybdenum, and thus the selectivity of the etching
process drastically decreases compared to the substrate 1110. The
lack of metal atoms during an etching process can be balanced by
adding a metal carbonyl as a precursor gas. FIG. 11 represents an
etching process 1800 in which the mixture of gases 1845 has a metal
carbonyl in addition to an etching gas (XeF.sub.2 in the present
case).
[0130] When using the metal carbonyls chromium hexacarbonyl
(Cr(CO).sub.6) and molybdenum hexacarbonyl (Mo(CO).sub.6) extremely
good results could be achieved, i.e., a significant acceleration of
the etching rate of the defect 1130, and thus an increase of the
etch selectivity. The application of other metal carbonyls is
however also possible. Furthermore, a combination of two or more
metal carbonyls can be used in the mixture of gases 1845.
Generally, the etching rate can be increased by increasing the gas
flow rate of the metal carbonyl(s). However, in this process it has
to be taken into account that metal carbonyls are deposition gases.
This means that the etching rate starts slowing down when a certain
gas flow rate of the metal carbonyl(s) is exceeded, since the
deposition portion starts outbalancing the portion of the
enhancement of the etching rate.
[0131] The ratio of the gas flow rates of the etching gas and the
metal carbonyl(s) can be adjusted to the composition of the MoSi
material of the defect during the etching process in order to
optimize the etching rate. The current composition of the etched
material can be determined from the energy distribution of the back
scattered and/or the secondary electrons of the detector 1030 of
the apparatus woo of FIG. 3.
[0132] However, the acceleration of the etching rate by the
addition of one or several metal carbonyl(s) to the etching gas
mixture 1845 does not lead to a decrease of the roughness 1242 of
the etched surface. The roughness of the etched surface can
drastically be reduced by the addition of water or water vapor
and/or by an ammonia providing gas.
[0133] As explained above, the reduction of the roughness is
accompanied by a slowing down of the etching process. Thus, the
ratios of the gas flow rates of the etching gas and the metal
carbonyl, on the one hand, and of the etching gas and water and/or
an ammonia providing gas, on the other hand, have to be optimized
as a function of the composition of the MoSi material of the defect
1130. In an extreme case, the etching process stops if the ratio of
the gas flow rates has the wrong size. The deposition effect of the
metal carbonyl outweighs the etching effect of the etching gas if
the gas flow rates of the metal carbonyl(s) and water and the
ammonia providing gas are too high relative to the gas flow rate of
the etching gas.
[0134] It is also possible to provide an etching gas and a metal
atom in a single gaseous compound similarly, as it has been
discussed in the context of the supply of an etching gas and a
second gas in a single compound. Exemplary compositions for this
process are: molybdenum hexafluoride (MoF.sub.6), chromium
tetrafluoride (CrF.sub.4) and tungsten hexafluoride (WF.sub.6).
Moreover, further metal fluoride compounds can be used for this
purpose. Finally, it is also possible to use other metal halogen
compounds in order to provide further etching chemicals on the
basis of further halogens apart from a fluorine-based etching
chemical.
[0135] The combination of an etching gas and a metal atom in a
single compound has the beneficial aspect to simplify the apparatus
1000 of FIG. 3 with respect to the storage of the respective
precursor gases. Moreover, the combination in a single compound
enables a more simple process control.
[0136] In a modified process control for increasing the metal
content during an etching process of a MoSi layer having a low
fraction of molybdenum, the metal carbonyl(s) are not added to the
mixture of gases during the etching process. Rather, a thin metal
layer made from one or several metal carbonyls is deposited prior
to the real etching process. The metal layer provides the metal
atoms which lack in the MoSi material during the etching
process.
[0137] The addition of metal carbonyls to a mixture of gases also
increases the etching rate of the quartz substrate 1110. Therefore,
the good localization of the metal atoms during the etching process
is an important advantage of the deposition of a thin metal layer
on the defect 1130 so that a trade-off with respect to the etch
selectivity can be avoided. For this reason, when using this
process control, one can do without the protection function of the
protection layer.
[0138] On the other hand, it is detrimental when using this process
control that the local provision of metal atoms from the metal
storage of the thin layer decreases in the course of the etching
process of the defect 1130, and thus the etching rate also
decreases. This disadvantage can be compensated by executing the
process in several steps, i.e., by periodically depositing a thin
metal layer.
[0139] After finalization of the etching processes 1400, 1600,
1700, or 1800 represented in FIG. 7, 9, 10, or 11 a cross-section
1900 through the mask 1100 has a protection layer 1955. When
compared to the protection layer 1150, the protection layer 1955
can have damages due to the effect of secondary particles 1460,
1660, 1760, or 1860 and/or the mixtures of the etching gas and the
second gas 1445, 1645, 1745, or 1845. FIG. 12 schematically
illustrates this by the partially removed protection layer 1955. On
the other hand, the defect has been removed by one of the etching
processes 1400, 1600, 1700, 1800 from the mask 1100, wherein the
surface 1150 of the substrate 1110 has essentially not be roughened
at the position of the defect.
[0140] FIG. 13 schematically shows the removal of a protection
layer 1955 of FIG. 13 remaining after the finalization of one of
the etching processes 1400, 1600, 1700, 1800. The protection layer
1150, 1955 is removed from the surface 1115 of the substrate 1110
by the use of an etching process by using an electron beam 2040 and
an etching gas 2045. Generally, for removing the protection layer
1150, 1955, etching processes are beneficial which have a high
selectivity with respect to the substrate 1110. In this sense,
fluorine-based etching gases are not desirable. Etching gases on
the bases of the remaining halogens, i.e., chlorine-, bromine-
and/or iodine-based etching gases have proved successful for
removing the protection layer 1150, 1955. Nitrosyl chlorine (NOCl)
is used as an etching gas 2045 in the etching process of FIG. 13.
The protection layer 1955 can be selectively removed from the
substrate 1110 of the mask 1100 by means of NOCl, wherein the
protection layer has been deposited from a metal carbonyl.
[0141] The protection layer 1150, 1955 deposited from one or
several metal carbonyls has additionally the beneficial
characteristic that it can residue-free be removed from the surface
1115 of the substrate 1110 with usual mask cleaning processes.
Thus, the etching process 2000 illustrated in FIG. 13 is not
needed. The protection layer 1150, 1955 is simply removed in the
course of one of the necessary mask cleaning steps.
[0142] FIG. 14 represents a segment 2100 of the mask 1100 after
finalizing the removal of the protection layer 1150, 1955. The
described repairing process has removed the defect of excessive
MoSi material without essentially damaging the surface 1115 of the
substrate 1110.
[0143] FIG. 15 schematically shows a segment of a substrate 2210 of
a photolithographic mask 2200. A line-space structure 2220, 2225
made from MoSi absorber material is applied to the surface 2215 of
the substrate 2210. The left line or stripe 2220 has a defect of
missing absorber material. The dotted line 2235 represents the
cutting line of the cross section through the segment of the
exposure mask 2200 of FIG. 15, which is illustrated in FIG. 16.
Prior to the repairing of the defect 2230, a protection layer 2150
is deposited on the surface 2215 of the substrate 2210 of the mask
2200 as it is schematically illustrated in FIG. 16. The protection
layer 2350 is deposited by the use of an electron beam 2340 and one
or more metal carbonyls or other volatile metal compounds as a
precursor gas 2345. In addition to metal carbonyls, for example
also wolfram fluoride (WF.sub.6), molybdenum fluoride (MoF.sub.6),
or further metal fluoride compounds can be used.
[0144] Details for depositing a protection layer 2350 have already
been explained when discussing of FIG. 5. It is the peculiarity of
the protection layer 2350 compared with the protection layer 1150
of FIG. 5 that the protection layer is not arranged adjacent to the
absorber element 2220 in the area of the cross section, but is
arranged a distance apart from the absorber element 2220 which
corresponds to the ground area of the defect 2230.
[0145] FIG. 17 schematically represents a deposition process 2400
for correcting the defect 2230. The deposition of the absorber
material which lacks due to the defect 2230 takes place by
providing one or several metal carbonyls 2445 at the position of
the defect or at the processing position or at the reaction site as
well as by means of an electron beam induced local chemical
reaction of the metal carbonyl(s) 2445 by the use of the electron
beam 2440. The electron beam 2440 splits the metal carbonyl(s)
2445. A portion of the separated CO ligands, or more general of the
non-metallic components, are pumped down from the reaction site by
the suction device 1085. The central metal atom of the metal
carbonyl or the metal atom of the metal fluorine compound is
deposited on the ground area of the defect 2230 together with
further fragments. Thus, a layer 2470 of absorbing material is
formed by repeated scans of the electron beam 2240 across the
ground area of the defect 2230.
[0146] The electron beam 2240 generates secondary electrons, or
more generally secondary particles 2460, similar to the etching
processes of FIGS. 6, 7 and 9-11. A portion of these secondary
particles will impinge on the protection layer 2350 and can split
the metal carbonyl particles which are available on the protection
layer, and can deposit a thin layer 2480 on the protection layer
2350 made from metal atoms and further fragments.
[0147] Chromium hexacarbonyl (Cr(CO.sub.6)) is a preferred metal
carbonyl for repairing the defect 2230. A layer of absorbing
material can also be grown by other metal carbonyls or by the use
of volatile metal compounds, for example by the above mentioned
metal fluorine compounds. In contrasts to the protection layer
2350, the absorber layer 2470 should adhere on the surface 2250 of
the substrate 2210 of the mask 2200 in the possible way, in order
that the protection layer 2350 is neither damaged by cleaning
processes nor by the exposure with ultraviolet radiation, and that
it is not detached from the substrate 2210.
[0148] The kinetic energy of the incident electrons is in the range
of 0.1 keV to 5.0 keV during the deposition process depicted in
FIG. 17. Beneficial beam currents comprise a range from 0.5 pA to
100 pA. The gas flow rate of the metal carbonyl(s) extends across a
range from 0.01 sccm to 5 sccm. The repetition time as well as the
dwell time has to be selected in a suitable manner so that the
etching rate is optimized.
[0149] FIG. 19 schematically represents the deposited absorber
layer 2555 and the thin absorber layer 2590 on the protection layer
2450 after finalization of the deposition process for repairing the
defect 2230. In the last process step, the protection layer 2450 is
again removed from the surface 2215 of the substrate 2210 in an
etching process 2500. As already explained in the context of FIG.
13, the etching process takes place with an electron beam induced
etching process whose parameters are explained above in the context
of the discussion of FIG. 13. In the etching process 2500 of FIG.
18, nitrosyl chlorine (NOCl) is used as etching gas 2545 similar to
the etching process of FIG. 13.
[0150] The protection layer 2350 of FIG. 18 can residue-free be
removed from the substrate 2210 of the mask 2250 using usual
cleaning processes, in an analog manner to the protection layer
1150 of FIG. 5.
[0151] Finally, FIG. 19 shows the segment of the mask 2200 after
finalization of the removal of the protection layer 2350. The
discussed correction process has essentially removed the defect
2030 of lacking MoSi material without damaging the surface 2215 of
the substrate 2210 of the mask 2200.
* * * * *